This invention pertains to a guard mechanism for production assembly machines which require hand manipulation of product materials in areas close to operating machine parts which can cause injury, and more particularly pertains to a guard for a shuttle type injection molding machine.
Many manufacturing processes include mechanical operations performed by automated machines which are preceded by the operator's hand manipulation of materials or equipment in hazardous areas close to machine parts which can cause injury to the operator. For example, the production of molded plugs on electrical cords is frequently performed by shuttle type injection molders which permit the mold operator to prepare the materials for one plug while another plug is being formed and cured in the mold. The mold includes one upper mold piece with a material injection ram, and two lower mold pieces on a shuttle carriage. The carriage moves in one direction or the other beneath the upper mold piece, to mate one or the other of the lower mold pieces with the upper mold piece as the upper mold piece is lowered toward the carriage at the beginning of the operating cycle. While material is being injected into the mold, and the curing process is carried out, the second lower mold piece, which is exposed and open, can be readied for the next plug formation. Hence, in the manufacture of electrical cords, while one plug is being formed, the mold operator can place the wires and terminals for another plug in the proper position in the open lower mold, and when the first mentioned plug is completed and the mold opens, another operating cycle can be started immediately to move the carriage and position the second lower mold piece beneath the upper mold piece. While the second plug is being formed, the completed product in the first lower mold piece can be removed, and materials for a third plug placed therein. In a typical shuttle injection molder, each cycle of the molding machine is initiated when the mold operator depresses a foot pedal, which begins a cycle wherein the carriage shift to move a lower mold piece beneath the upper mold piece, the upper mold piece is lowered and mates with the lower mold piece, material is injected into the mold, the injected material is cured, and the mold is opened. A single depression of the foot pedal begins the cycle, which continues uninterrupted until the mold opens after curing has occurred.
One of the problems encountered with shuttle type injection molders is that, as the carriage moves, materials placed in the lower mold piece, such as, in the example, the wires and terminals of an electrical plug, may become slightly mispositioned. The natural and almost instantaneous reaction of the molding machine operator is to reach for the lower mold and correctly position the materials therein. Danger arises in that once the operating cycle of the machine begins, it continues to completion, and if the mold operator, in his attempt to reposition the materials in the lower mold, places his fingers between the upper and lower mold pieces and the mold closes, the operator's hand can be severely injured. Emergency stop circuitry is provided for the molding machine which, upon depression of an emergency button, will interrupt the mold cycle and open the mold; however, since accidents of this type normally occur relatively quickly, the operator is usually unaware of the danger until after the injury has occurred. Although he may be able to press the emergency button and open the mold before completion of the operating cycle, normally this will not be done until the mold has closed fully and the injury has occurred.
It is known in the prior art to provide guards in the area of the carriage, which, if moved from a neutral position, prevent operation of the foot pedal to start the operating cycle. These previous devices have not been completely satisfactory, however, in that on shuttle molds having relatively long carriages, the mechanical linkage of the previous guards has been such that, to operate the interrupt circuitry of the guard devices, deflection at the far end of the guard must be relatively extreme, often more than occurs from an errantly placed finger or hand. Another problem with the previous devices has been that only interruption of the operation of the foot pedal occurs; the actual mold cycle, once initiated, is not broken. Hence, if the foot pedal is depressed to start the cycle before the interrupt circuitry is activated, the mole will continue through its cycle and injury to the operator can occur. The previous devices are useful only in situations wherein the interrupt circuitry is activated prior to an attempt to initiate the mold cycle, in that the previous devices prevent the start of the cycle but do not interrupt the cycle once it has begun.